Velocity modulated tube



Dec. 8, 1942. c. v. LlTTON VELOCITY MODULATED TUBE Filed Dec. 14, 1939 4 Sheets-Sheet l QWN INVENTOR.

C'f/fl/Pll? 144/770 ATTORNEY.

Dec. 8, 1942. c v, oN 2,304,186

VELOCITY MODULATED TUBE Filed Dec. 14, 1959 Sheets-Sheet 2 'vz'fz' "V L l ATTORNEY.

1942. c. v. LITTON 2,304,186

VELOCITY MODULATED TUBE I I 7 Filed Dec. 14, 1939 4 Sheets-Sheet 3 ms. 655 I ummismsPATENT m to International Standard Calm, alllmr mm 00 tlon, New York, N. Y., a corporation-of Dela- Application 14, 1939. 8am No.3,174 4 Claims. (Cl. 250-215) My invention relates to vacuum tubes. and more particularly to vacuum tubes for ultra-high frequency operation wherein a stream of: electrons is deflected longitudinally for the purpose of generating or amplifying high frequency oscillations;

In a known form of vacuum tubes a stream of electrons emitted from a cathode is given a longitudinal velocity in a particular direction and means is provided for altering the relative velocity of some of the electrons in the stream with respect to others at a. particular point along the stream. By further progress along this longitudinal direction the electrons become grouped. A further means spaced along the longitudinal direction of the stream is then provided for extracting energy from-the grouped electrons, the frequency of the energy depending upon the periods of the groupings thereof.

It is a principal object of my invention to provide a tube operating on the principles outlined above, which is simple in construction and reliable in operation, has a low loss, produces a high power output and has other desirable characteristics.

It is a further object of my invention to provide a tube structure for operation upon or generation of ultra-high frequency waves having built-in circuits wherein means is provided for.

exactly tuning the circuits within said tube by external adjusting means.

It is a still further object of my invention to provide a tuning indicator by which visual ob.- servation of the resonant condition of the tube may be made.

It is a still further object of my invention to provide a cathode structure which will permit maximum power output.

It is further contemplated in accordance with my invention to construct tubes of the type outlined above wherein potentials may be supplied to the different grids thereof independently one of another.

It is a still further object of my invention to provide control feedback arrangements within or external of said tube together with means for adjusting the amount orphase of the feedback.

Other objects and advantages of my invention will be apparent from the particular description thereof made in connection with the accompanying drawings In which- Fig. 1 illustrates the preferred structural arrangement of a tube embodying many of the features ofmy invention,

Fig. 2 illustrates a preferred cathode structural arrangement utilized in the tube shown in Fig. l,

tending beyond the end thereof is provided a Fig. 3 illustrates the heating filament i'orthe cathode of Fig. 2,

Fig. 4 illustrates the particular of grid for utilization in the tube,

Fig. 5 illustrates a modified cathode and grid assembly in accordance with my invention,

Fig. 6 illustrates a modified type of tube in accordance with my invention, wherein the oscillating circuits are insulated one from the other,

Fig. 7 illustrates a still further modification wherein a common wall is provided between the two chambers and an externally adjustable back coupling arrangement is provided,

Fig. 8 illustrates a still further modified form of the tube construction wherein a water cooling of the entire tube may be formed by a simple water jacket and wherein the feedback may be accomplished by means of a coupling line connected directly with the load line, and

Fig. 9 illustrates a combination of tube structure of the type shown in Figs. 5 and 6, substituted for corresponding parts in the form of tube shown in Fig. l.

In Fig. 1 a vacuum tube incorporating features in accordance with my invention is illustrated. This tube comprises generally a cathode assembly I00, a grouping grid-and-circuit assembly designated generally at I30, an extracting grid-andcircuit assembly designated generally at I60, and a tuning resonance indicator indicated generally at I 80. Circuits I30 and I are tuned to resonance at the operating frequency. The cathode comprises a heating filament IOI connected over leads I02 to a suitable power source, these leads being brought through a glass sealing member I03. Member I03 is sealed to a tube I04 preferably of copper, which in turn is firmly secured to member I05 preferably made of hardened alloy steel. Member I05 is held firmly against a fur ther member I06 preferably also of hard ground steel alloy. Annular grooves preferably about .005" wide and .002-.005" deep, are provided on the faces of each member, and between these members preferably is provided a gasket of some soft metal such as aluminum. Fastened to members I06 is a wall member I01 forming a part of the envelope of the vacuum tube structure. Supported on a ring I08 clamped about stem I03 is indirectly heated cathode I09. The end surface of this cathode is preferably coated with a metallic oxide such as barium and strontium oxide so that it will more readily produce strong electron streams. About the cathode I09 and expreferred formcathode potential distributing shield IIO maintained at cathode potential.

I have found that when an ordinary spiral cathode filament is used, in this type of tube, the magnetic field from the cathode tends to disperse the electron beams, as is evidenced by the fact that when the current is momentarily turned off the output increases several fold. In order to overcome this diiliculty I provide in accordance with my invention a heater winding wound noninductively as shown in Fig. 3. This filament is preferably made by a bifilar wound wire so that the inductive effect of the winding is substantially completely eliminated. By use of such a filament it has been demonstracted that the power output of the tube is increased two or three times.

Circuits I30, I60 are given a high potential to tend to accelerate an electron stream emitted from cathode I09 to a high velocity. Circuit I30 is tuned substantially to the operating frequency of the tube and consists of an annular resonant chamber I3I at the center of which is provided grids I32 and I33. Since circuit I30 is oscillating at a high frequency, grids I32 and I33 alternate in potential with respect to each other at the operating frequency. As a consequence the electrons passing between these grids are periodically accelerated and decelerated depending on the instantaneous field between the grids. The electron stream then passes onward from these grid circuits over a space between the grid I33 of circuit I30 and grid I62 of resonant circuit I60. Circuit I60 is preferably likewise tuned to the resonant operating frequency. Since the space between grids I33 and I62 is in the order of wavelength long, the electrons tend to fall into groups while traversing the space, the accelerated electrons advancing while the decelerated electrons are retarded with respect to the initial electron stream velocity.

The electrons then upon reaching grid electrode I62 pass through electrodes I62 and I63 in groups. The spacing of the electrodes is so chosen that these electron groups are in phase opposition with the oscillations in I 60 upon reaching grids I62, I63. Energy is thus extracted from the groups as they pass therethrough and the electron stream as a whole is highly decelerated. Thus energy is released in circuit I60, the energy of which may be extracted therefrom by means of a load line I10. Beyond grid I63 a target electrode I15, for example, of copper, is provided. This target electrode is preferably maintained at a potential lower than the potential applied to the grids so that the decelerated electrons will be attracted thereto, the potential being such that the electrons will not have sufiicient velocity to cause production of secondary emission, but are retained by the target so that they will not be deflected back to the grids to cause large current at hi h potential, heating of the grids, and random distribution, with consequent loss in efliciency; This potential may, for

complete description of the remaining parts of the system explaining the structural arrangement more in detail follows.

The walls of the tube I01 are connected directly with a further metallic wall, preferably copper, III, which provides a direct connection to the walls of resonant chamber I30. The walls I35 of chamber I3I to which grid I32 is fastened is preferably made of reduced thickness so that it may be deformed longitudinally. Fastened to grid I32 is a tube I36 upon which is provided one or more, preferably two, extending pins or lugs I31. A lever I20 is pivoted at one end and provided with a slot to accommodate pins I31. The other end of lever I20 is connected by means of a link mechanism I2I to a screw adjustable cap I22. Link I2I preferably forms the closure end for a metal bellows I23 so that the link may be displaced longitudinally within the vacuum tight tube chamber. By rotating cap I22, link I2I may be varied in position, locking lever I20 and thus moving grid I32 relative to grid I33. This adjustment of the relative spacing of grids I32 and I33 aids in the tuning adjustment of the circuit.

Normally resonators I30 and I60 are made as nearly identical as possible in characteristics as originally constructed. However, it is not always possible to make them duplicates. For this reason a vernier tuning adjustment is necessary in order that the circuit be exactly tuned to resonance. The movement of grid I32 by the adjusting means described above operates to perform this desired function by changing the spacing between I32 and I33.

When the tube, as described above, is to function as an oscillation generator it is necessary to provide a feedback coupling between resonant chambers I60 and I 30; This feedback is accomplished in accordance with the circuit illustrated in Fig. 1 by means of a link circuit I50 provided with a loop at each end, one in chamber I60 and one in chamber I30. To adjust the amount of energy fed back, I provide a sealed arrangement for rotating link I50 to vary the coupling of the loop. This may be accomplished within the evacuated chamber by mounting link I 50 on a toothed gear I5I. Cooperating with this gear is a rack I52,- the other end of which forms the closure end for another metal bellows I53. Metal bellows I 53 is adjusted by means of a screw cap I54 similar in construction to that to cap I22 previously described. By rotating-cap I54 the rack may be moved forward or backward changing the position of the link I50 and the loop thereon so as to vary the coupling. However,

the amount of feedback does not appear to be critical to the operation of the system, and therefore the adjustment feature may be omitted if desired. a

To extract energy from resonant circuit I60, I provide a simple metal to glass seal arrangement as shown generally at load line I10. This load line comprises a concentric conductor arrangement having an outer wall "I and a central conductor I12. The inner conductor is fastened to a metal stem I13 by screw threads, this member I13 being sealed to glass sealing member I14. The other end of member I14 is sealed to a further metal tubular member I15 which in turn is fastened to a screw threaded member I16. Another conducting member I11 is fastened to member I13 and is provided with a small loop which is conductively connected to the outer wall of resonant chamber I60. Member I16 is then threaded into the wall of member I60 at a point spaced from the fastening point of conductor "1, thu forming within the chamber a loop for picking up energy therefrom. By this arrangement a simple easily formed seal is provided wherein only a single metal, such as copper, is used. This line is preferably of such characteristics as to present substantially a constant impedance load to the circuit. This may be achieved by calculation of the dimensions, i. e., the diameter of the metal parts, and the dielectric constants of the glass in the seal, so that a constant impedance may be maintained.

When the tube is used as an oscillation generator, the energy generated therein is taken therefrom by means of line I10. When the tube is used as an amplifier circuit the coupling link I50 may be omitted and in its stead an input coupling link similar to that disclosed at may be provided for supplying energy to resonant circuit I30. Furthermore, if it is desired to apply different direct current potentials to the resonant chambers I30, I60, this may be accomplished by providing an insulating strip in the walls of the tube to separate these circuits one from the other electrically.

In order that the resonant operating condition of the system may be observed, I provide in target electrode I15 and centrally thereof, a small hole or aperture I16, through which some electrons from the stream may pass. A fluorescent screen I8I preferably of mica is mounted in the path of these electrons, and externally of this screen a glass window I82. When the circuit is not properly tuned to resonance the electrons passing through aperture I I6 and impending on screen I8! produce a very small spot. However, when the circuit is tuned to resonance the velocity of electrons passing through the aperture will be greatly reduced so that upon striking screen I8I they will no longer be concentrated in a small bright spot but will form a larger difi'used spot of illumination thereon. Consequently a direct observation of the resonant condition of the circuit may be obtained. I

While I have illustrated a preferred embodiment of my invention as shown in Fig. 1, a separate target I15, it should be understood that the operation of my system does not depend upon such an arrangement. If desired, in place of grid I63 may be provided a target electrode such as I75. However, this arrangement is not preferred, since it would then require that a high potential be applied to this electrode as well as to the grid electrodes. Accordingly, greater heat losses would occur and the eiiiciency of the system would be somewhat lower.

As shown in Fig. 1, the tube structure is provided with a T connection I 90 to which a vacuum pump may be connected. It isclear that this pump may be connected at some other point, for example down near the end of the cathode tube or the tube may be evacuated and sealed off. In such an event the entire system may be provided with a cooling water jacket so that the same cooling system will apply to the target electrode I15 and to the other portions of the tube.

Although I have not illustrated the cooling jacket for the tube envelope proper, it is clear that such a system may be provided. In accordance with my invention, with a tube such as shown in Fig. 1, I preferably provide a water jacket made of tubing arranged in a zigzag formation around the periphery of the'main body of the tube. This zigzag arrangement is preferably maintained symmetrically endwise with respect to the tubes. In a particular construction of this tube arrangement, the water jacket is formed of quarter inch copper tubing arranged as described above, the pitch of the zigzag formation being about 2" and the amplitude thereof about 3".

In Fig. 5 is shown a fragmentary view of a portion of the tube illustrating a modified structural arrangement for adjusting the spacing between grids I32, I33. According to this arrangement grid I32 is mounted directly in a metal tubular element 50 I, which may serve as a part of the tube envelope. Within element SM is provided the cathode unit assembly I00. Element 50I is sealed directly to the glass stem portion I03 to produce a vacuum tight joint. A thin wall or diaphragm I35 is provided in-the wall of resonant chamber I3I. A screw threaded ring 502 is threadedly engaged with the outer surface of tube I I to permit longitudinal movement thereof. Operatively associated therewith by means of ball joint is a ball ring 503. Ring 503 is provided with spider supports 504 upon which the resonant chamber I3I is supported. By rotating ring 502 the entire cathode assembly'together with grid I32 may be moved closer or further away from the grid I33, lug 5I0 serving to hold the assembly in unit-handling relationship. With thisarrangement a vemier adjustment may be accomplished without the use of the metal bellows arrangement I 23 of Fig. 1.

Further, I have illustrated in Fig. 5, tube 505 about the outer surface of the cathode which may be used for cooling the cathode and preventing overheating thereof. It should be understood that thiscathode cooling arrangement may be applied equally to the structure of Fig. 1 and other embodiments of my invention.

In Fig. 6 is illustrated diagrammatically a modified structural arrangement. In accordance with this figure, chambers I30 and I are insulated from each other centrally by means of insulating bushings 600. When so insulated separate control potentials may be applied to chambers I 30, I60.to adjust the operational characteristics of the tube. With this connection, however, direct feedback of the type illustrated in accordance with Fig. 1, may not be used since such a feedback circuit would operate as a metallic coupling between the circuits. Accordingly, I provide an external coupling link- 650, with loops I, 652 in chambers I 30, I60, respectively. An insulating bushing, for example of glass, 655, is provided about the conductor leads so as to preserve a direct current isolation between the portions of the circuit.

In Fig. 7 is shown a still further modification of tube structure in accordance with my invention. According to this arrangement resonant chambers I30, I60 are provided with a common dividing wall 700. The load line I-I0 similar to that shown in Fig. l is provided. The feedback circuit is made externally and comprises two concentric leads 'i0l, I02 similar in construction to the coupling arrangement I'I0. These two concentric conductors are slidably joined with trombone slide element 703 so that a rela ive phase adjustment of the energy fed back may be achieved. It is clear that this feedback arrangement if des red may be utilized with the circuit shown in Fig. 1 in place of the internal feedback arrangement disclosed therein, or with other structural embodiments. Since the leadout arthat if desired the construction similar to that shown in Fig. '1 utilizing a separate target electrode may be provided.

In Fig. 8 is shown still another embodimentof my invention. In accordance with this arrangement separate resonant chambers I30, I60 are not conductively connected at their outer periphery as shown in Fig. l, but instead form a vacuum chamber with the tubes interconnecting grids I32, I33, I62, "I63. About the whole assembly a common water jacket 800 is provided so that the entire system may be readily water cooled. Connected with resonant chamber I60 is a large loop 80I which serves to obtain energy from this circuit in a manner similar to the tubes I" of Fig. 1. A similar but smaller loop 0012 is provided in circuit I30 and this loop 002 is directly connected with loop BOI so that a portion of the energy derived through 80I is fed back through loop 302 to maintain the oscillation. The loop 602 is made considerably smaller than I, since it is desirable that the major portion of the energy be transferred to the load over line 804. It is manifest that if desired, the line interconnecting loops 80I and 802 may be made adjustable, in the manner described in connection with the showing of Fig. 7. It is also clear that the modified arrangement of Fig. 8, whereby a common water cooling jacket is supplied for the entire system may be readily applied to the other circuits illustrated in the preceding figures if desired.

Fig. 9 shows the cathode assembly and associated elements of Fig. 5, combined with the resonant shells I30 and I60 of Fig. 6, the resulting arrangement being substituted in place of the corresponding cathode assembly and resonant shells in Fig. l, the operation being obvious from the detailed description already given in connection with Figs. 1, 5 and 6.

In describing the various figures outlined above mention has been made of the grids I32, I33, I62, I63 of the system. A preferred structural arrangement for the grid in accordance with my invention is illustrated in Fig. 4. This grid is preferably of tantalum of thin dimension, and consists of two concentric annular strips 400, l0I between which are disposed a plurality of radial strips 402. In an actual structural arrangement of such grids, the grid was made of tantalum .004" thick and a quarter of an inch wide. The grids were made of strips bent to form a central cylinder of diameter and the outer ring, the strips being so arranged that the radial crossing occurred at 30 intervals.

While I prefer a tantalum grid or similar metal grid constucted as above indicated, if desired the grid may be made of metal such as copper cast or fabricated to the desired form.

While I have described a few preferred embodiments of my invention it is to be distinctly understood that these are given merely by way of example. It should be further understood that the various modifications illustrated may be utilized one with the other in various combinations without departure from the scope of my invention.

What 1 consider to be my invention and desire to obtain protection upon is embodied in the accompanying claims.

What I claim is:

1. A vacuum tube structure according to claim 4, wherein said cathode comprises a noninductively wound heater filament whereby electro-magnetic influence of said filament on said electron stream is reduced, and an electron emitting member arranged to be heated by said filament.

2. A vacuum tube comprising a first annular shell resonant at the operating frequency of the tube and having apertures centrally on opposite sides thereof, a cathode assembly, a first generally tubular metal member insulatingly sealed to said cathode assembly and sealed to said first annular shell at one aperture thereof, a second annular shell resonant at said operating frequency and provided with an aperture centrally thereof, a second tubular member interconnecting said first and second resonant shell sealed to said first shell at the other aperture thereof and to said second shell at the aperture thereof to provide an airtight seal, whereby the envelope of said tube comprises said annular shells, said cathode assembly, and said first tubular member and said second tubular member, a pair of electron velocity control grids in said first resonant shell mounted on the ends of said first tubular member and said second tubular member respectively, and a work grid mounted on the end of said tubular member within said second resonant shell, said second tubular member being provided with an insulating means interrupting the conductivity thereof at a point intermediate said first and second resonant shells.

3. A vacuum tube comprising a first annular shell resonant at the operating frequency of the tube and having apertures centrally on opposite sides thereof, a cathode assembly, a first generally tubular metal member insulatingly sealed to said cathode assembly and sealed to said first annular shell at one aperture thereof, a second annular shell resonant at said operating frequency and provided with an aperture centrally thereof, a second tubular member interconnecting said first and second resonant shell sealed to the said first shell at the other aperture thereof and to said second shell at the aperture thereof to provide an airtight seal, whereby the envelope of said tube comprises said annular shells, said cathode assembly, and said first tubular member and said second tubular member, a pair of electron velocity control grids in said first resonant shell mounted on the ends of said first tubular member and second tubular member respectively, and a work grid mounted on the end of said second tubular member within said second resonant shell, a further tubular member extending into a second aperture provided centrally in said second resonant shell, 9.

second work grid mounted in said second resonant shell on said further tubular member, and a further electrode mounted beyond the end of said further tubular member, whereby energy remaining in said electrons may be dissipated into said electrode after passing through said second resonant shell.

4. A vacuum tube comprising an evacuated envelope, elements within said envelope including an electron emitting cathode, a pair of grids coupled to a first hollow resonator resonant circuit and mounted in the path of the electron stream emitted from said cathode for varying the relative velocity of electrons in said stream,

a second grid means spaced longitudinally along said electron stream from said first mentioned pair of grids and coupled to a second hollow resonator resonant circuit for deriving energy from the electrons passing through said second grid means, means coupled to said second resonant circuit for extracting energy from said circuit, means external to said tube envelope for adjustably relating the spacing between the grids of said first pair for adjusting said circuits to resonance with one another, a plate electrode for receiving the electrons of said stream after passing said second grid means, said plate electrode being provided with a central aperture for passing some electrons from said stream, a fluorescent screen in the path of said electrons that have passed through said aperture, and transparent means mounted externally of said screen for visual observation of said fluorescent screen, whereby a resonant condition of said circuit may be observed.

CHARLES V. HTI'ON.

DISCLAIMER 2,304,186.Oharles V. Litton, Redwood City, Calif. VELOCITY MODULATED TUBE. Patent dated-December 8, 1942. Disclaimer filed April 19, 1943, by the assignee, International Standard Electric Corporation. Hereby enters this disclaimer to claim 4 in said specification.

lofiim'al Gazette Mag/11, 1943.]

DISCLAIMER 2,304,186.Oharles V. Litton, Redwood City, Calif. VELOCITY Monm'mn TUBE. Patent dated Dec. 8, 1942. Disclaimer filed May 8,1945, by the assignee, International Standard Electric C'orporatqkm. Hereby enters this disclaimer to claim 3 of said patent.

[Qfl'icial Gazette June 12, 1945.] 

